To perform the control function, electromechanical relays are being used which make it possible to stop current flow through the glow plug in the event a short-circuit is detected.
However, these electromechanical relays have a high response time, on the order of several milliseconds, so they are not able to open the circuit with the speed required, and damages due to overcurrents may occur in the few milliseconds in which the relay is still closed and the short-circuit exists.
Certain known control devices of this type already incorporate semiconductors to reduce the response time, such as those presented in U.S. Pat. Nos. 5,122,968 and 4,500,775 and German patents nos. 38.06.649 and 40.04.400.
In some of these known devices, the glow plugs are connected in parallel whether in groups or the entire set, making diagnosis of failures difficult precisely because of this connection.